When one person says no, it gets a lot easier for everyone else to say it too.

In a group, nobody wants to be first. Most people in the room have reservations and are each assuming they are the only one, so the silence gets read as agreement and the thing goes ahead. One plain refusal breaks that, because it turns out several others were waiting for permission. You are not persuading anyone, you are just going first.

If something is heading somewhere you are not comfortable with, say so simply and without a speech: I am not doing that. Say it early, before the group has committed, since that is when it costs least. Watch how often someone else immediately agrees.